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Add a ListBuilder helper for constructing list values

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Previously, `state.mkList()` would set the type of the value to tList
and allocate the list vector, but it would not initialize the values
in the list. This has two problems:

* If an exception occurs, the list is left in an undefined state.

* More importantly, for multithreaded evaluation, if a value
  transitions from thunk to non-thunk, it should be final (i.e. other
  threads should be able to access the value safely).

To address this, there now is a `ListBuilder` class (analogous to
`BindingsBuilder`) to build the list vector prior to the call to
`Value::mkList()`. Typical usage:

   auto list = state.buildList(size);
   for (auto & v : list)
       v = ... set value ...;
   vRes.mkList(list);
This commit is contained in:
Eelco Dolstra 2024-03-14 19:10:31 +01:00
parent bff5c94184
commit fecff520d7
10 changed files with 228 additions and 157 deletions
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8
src/libexpr/primops/fromTOML.cc
View file

@ -38,10 +38,10 @@ static void prim_fromTOML(EvalState & state, const PosIdx pos, Value * * args, V
{
auto array = toml::get<std::vector<toml::value>>(t);
size_t size = array.size();
state.mkList(v, size);
for (size_t i = 0; i < size; ++i)
visit(*(v.listElems()[i] = state.allocValue()), array[i]);
auto list = state.buildList(array.size());
for (const auto & [n, v] : enumerate(list))
visit(*(v = state.allocValue()), array[n]);
v.mkList(list);
}
break;;
case toml::value_t::boolean: